The placing of electrical current on a moving wire is currently required and is being done in at least the electrical discharge machine (EDM) industries and welding industries. This is currently normally accomplished by providing various shaped current pickups which are electrically charged. The moving wire slides or rubs against the electrically charged surface of the current pickup thus transferring electrical current therethrough to and from the moving wire. One common pickup is generally cylindrically shaped with a bore therethrough. The wire is received through the pickup bore and, because the current pickup bore is offset from the straight line of wire travel, the moving wire electrode rubs against the interior surface of the bore making the necessary electrical contact for transferring current to the moving wire. Other current pickup devices are made with various shaped contact surfaces and are pushed toward the taut moving wire electrode or placed in the normal straight line of wire travel causing the wire to rub against the current pickup contact surface thereby making the necessary electrical contact. Current pickups such as those described hereinabove are, for example, disclosed in U.S. Pat. No. 4,896,013 and U.S. Pat. No. 4,539,459.
However, the current pickups which are presently known and used have substantial shortcomings and drawbacks. Like all current pickups, as the moving wire slides against the pickup contact surface, the current pickup tends to wear and the wire causes a groove to be formed in the pickup through the original contact surface. Once the groove becomes sufficiently large in depth, the wire tends to bind therein causing wire breakage and requiring the stopping of, for example, the EDM operation and re-threading of the wire. As the groove is formed, the wire also tends to get closer to the normal straight line of wire travel (straighter) and even though the wire remains taut, there is insufficient contact between the wire and the new contact surface at the bottom of the groove for efficient current transfer. In view of this, after a particular contact surface has worn by a predetermined amount, the current pickup position is changed so as to provide a new contact surface or the entire current pickup itself is replaced.
Prior current pickups, however, provide relatively few contact surface positions whereat a new contact surface can be exposed to the moving wire. Typically, the cylinder-shaped pickups have a bore diameter only slightly larger than the wire diameter and, therefore, the maximum number of contact surfaces is four. Each of the contact surfaces for these current pickups are located on the current pickup bore surface at 90 degrees from each other with respect to the bore longitudinal axis. After these four contact surfaces have been exposed and worn, the current pickup is no longer useful and is replaced. Exposing the four different contact surfaces of the cylinder-type pickups, however, normally requires the disassembly of the various guide arm assembly components so as to gain access to the current pickup located therein and so that a tool or other means can be used for turning the current pickup about its longitudinal axis and exposing the new contact surface. An example of this is disclosed in U.S. Pat. No. 5,089,680. As can be appreciated, although this is generally acceptable, the disassembly of the entire guide arm to gain access to the current pickup can be cumbersome, time-consuming and, thus, costly. In addition, although other devices such as those disclosed in U.S. Pat. No. 4,994,643 have been devised for tilting and/or turning the cylindrical-type current pickup without disassembly of the entire guide arm, such devices of the past are somewhat complex and costly. Furthermore, even with such devices, the replacement of the current pickup, once all bore contact surfaces have been diminished still requires complete disassembly of the guide arm for gaining access to the current pickup and replacing the same. Again, this is somewhat cumbersome, time-consuming and costly.
Accordingly, a need exists for a current pickup apparatus that conveys electrical current to and from a moving wire and which overcomes the above-discussed disadvantages associated with prior current pickup assemblies and which further provides a substantial number of different contact surfaces on the pickup and which allows easy removing and replacing the pickup without disassembly of the guide arm assembly housing the pickup. In addition, a need exists for such apparatus which is both reliable and generally inexpensive to manufacture, assemble and operate.